One thing that all Mini owners should know how to do, beyond knowing how to completely disassemble the carbine for a deep clean, is to be familiar with removing the extractor.
If you ever have to replace an extractor, or even take out the firing pin for cleaning and inspection, you'll need to know how.
It's not that difficult but can be frustrating due to the tension of the extractor's plunger spring. You'll feel like you need an extra hand, and if that's what's needed, nothing wrong to have someone help.
I'm sure there are videos and threads somewhere about it, but it's something I feel everyone should know.
The extractor and the firing pin get a lot of abuse, especially so if you fire much Berdan primed steel case Russian ammo.
Other parts on a Mini get abuse too, but they are bigger more robust parts.
I can't think of other spare parts for a Mini that I feel the need to keep in stock besides the extractor, extractor plunger and it's spring, and firing pin.
Maybe a spare magazine release spring, as having that go bad would turn your semi auto into a single shot if your mags won't stay in.
But springs can be easily matched, find a similar diameter one, cut it to length if needed and you are back in business.
I carry on both my Mini's, a Spectre Gear magazine pouch on the butt stock that has a zip lock bag containing an Otis cable and some cleaning gear, several small Allen wrenches to fit the Tech sight, Ultimak and my gas block screws, a spare extractor, extractor plunger and spring and pre fitted spare firing pin, and a broken shell extractor, in case you have a case break off and is stuck in your chamber.
In good times like now, you can just send your Mini back to Ruger and not only will they replace a missing part, will probably do it for free.
But some of us, myself included, are handy, like to tinker and are comfortable doing our own minor repairs.
I won't send my Mini's in for something minor that I can fix myself for $4 and a few minutes of my time.
In bad times, like a SHTF breakdown of society scenario, you won't have the US mail or UPS running, so would have a hard time sending your Mini back to Ruger, or even being able to have a spare part shipped to you.
Even if you can get a local gunsmith to repair your Mini, he might be knowledgeable enough, but wouldn't likely have much in the way of spare Mini parts in stock.
I find it a bit easier to remove the extractor, without needing that third hand, to place a punch or other small rod sticking up out of your vise an inch or two.
The bottom of your extractor will appear as a circle on the bottom of your bolt, near the front, like this:
You need to push down on the extractor plunger so it's not against the extractor. Since there's not a ready made tool for this like the AR guys have, I use a small jeweler's screwdriver. You have to get the right angle on it as it want's to slip off the plunger more than not.
Holding the bolt in one hand, and the little screwdriver in the other, rest the bolt down so the "circle' on the bottom of the bolt ( the bottom of the extractor) rests on the top of your punch tip sticking up out of the vise.
Now push down the plunger with the screwdriver tip, and the extractor will start rising up out of the bolt.
Before the extractor is up too far, restrain the plunger or the spring under it will launch it across the room.
Now that the extractor, plunger and spring are out, the firing pin will slide out the back of the bolt, and it can be inspected and the channel it rides in inside the bolt can be cleaned. When reassembling, don't put oil inside the channel or on the firing pin, but some Dri-Lube like Rem-Dri is O.K.
Reassembly is the reverse, just make sure that the plunger is back the same direction so it rests against the extractor properly.
You don't want to have the plunger in twisted or the extractor won't be able to flex it's full range.
Get on Midway's, Brownell's or gunpartscorp's website now, and order a couple spare extractors, plungers and springs, it won't set you back much.
Then you'll have them on hand.
Practice taking the extractor out and putting it back in till your comfortable with it. You don't need to be able to do it blindfolded while under fire, but being comfortable with changing one out at home will make it easier if you have to do one out in the woods with only a flat rock for a table.